17. Air and Water Transport
17.1 Air Transport
It is less than 100 years since the flight of the first
powered, heavier-than-air machine in 1903. However air transport now plays
a vital part in the transport system of most countries.
Today, air transport is the major public transport
carrier of inter-capital city passengers, and plays a major role in intra-state
passenger transport.
Air transport has two distinctive characteristics:
- it is the fastest mode of transport available
over long distances (due to use of a very fast moving vehicle and an almost
direct line of travel); and
- it is generally the most expensive mode of transport
over any distance.
These two characteristics have led air transport to
specialise in transporting passengers and high value commodities.
17.2 Air Traffic Control
The task of air traffic control is basically to prevent
aircraft from colliding by ensuring orderly and safe take-off, flying and
landing operations. To do this two things are necessary:
- the position of each aircraft must be known
at all times; and
- safe separation distance between aircraft must
be established and maintained. The problem of fixing the position of an aircraft
may be complex.
The accuracy of defining the position depends on the
nature and reliability of available equipment; the aircraft’s distance from
the position fixing equipment; the weather; and the time of the day. The
error in fixing the position of an aircraft can often be large – up to the
order of several kilometres. Therefore every aircraft flies in its own
volume of uncertainty, and it is the task of air traffic control to prevent
the volume of uncertainty of different aircraft overlapping.
Air traffic control usually divides airspace into
one of three types:
- terminal airspace, in the vicinity of airports,
where movements are controlled by ground located air traffic controllers;
- airways, which are designated flight paths
between terminal airspaces or airports; and
- uncontrolled airspace.
Aircraft flying outside terminal airspace operate on
either visual flight rules (VFR) or instrument flight rules (IFR). In visual
flight rule mode it is the pilot’s responsibility to make visual contact
with other aircraft i.e. it works on the principle of ‘see and be seen’.
A flight begins with the pilot filing a flight plan
which details departure time, flight route, altitude, destination, etc. The
flight plan must account for the anticipated weather conditions along the
route, and the load to be carried. When the flight is ready to commence the
air traffic controller advises the pilot by radio when taxiways and runway
may be used. Once the aircraft is airborne a climb-out path from the airport
is indicated by the air traffic controller. This climb-out path depends on
factors such as the aircrafts performance and load, wind speed, and restrictions
on noise, etc. On reaching a predetermined height the aircraft turns onto
the first airway and climbs to cruising height.
Aircraft flying along airways in opposite directions
are separated in altitude:
- up to 8700m, by 300m; and
- above 8700m, by 600m.
As the aircraft approaches its destination it again
enters terminal airspace and is controlled by ground based air traffic control.
If congestion occurs in the use of runways at the airport, incoming aircraft
will be held in stacking areas, which are usually oval shaped, about 8km
long and 5 km wide. The aircraft will circle in these stacking areas, separated
vertically by about 300m, until directed to move down the stack or to land
by air traffic control.
LINKS TO SITES ON AIR TRAFFIC CONTROL.
The airtraffic control system in Australia is outlined
in the Parliamentary Background Paper '
Airspace Safety: Air Traffic Control and Airline Operations in Australia
' by Matthew L. James.
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17.3 Airports
Airports are a key element of air transport. They encompass
a variety of air and ground activities. The efficiency of operation of airports
is very important from economic and safety viewpoints, particularly in large
city airports where most aviation activities occur. Today, air traffic congestion
at major airports is one of the critical problems facing the future of air
transport.
17.3.1 Site Selection
The task of selecting an acceptable site for a new
airport can be very difficult. Not only must technical, economic and financial
factors be considered, but the often intangibles of social, political and
environmental issues must be addressed. This is particularly true in areas
where population density is reasonably high and/or where land use is intense.
The technical factors to be considered include:
- Safety Factors
- Topography
- Foundation Conditions
- Usability
- Noise
- Extension Possibilities
- Navigational Aids
- Land Use Compatibility
17.3.2 Runway Configurations
Each runway is numbered, indicating its magnetic alignment.
For example an east-west runway would be designated 09–27: 27 at the eastern
end (270×); and 9 at the western end (90×).
The choice of runway configuration depends on a
number of factors, including:
- Traffic
- Wind
- Slope
- Avoidance of Bird Hazards
- Runway Length
- Environmental Factors
17.3.3 Runway Length
The length of runway required depends on:
- the type of aircraft which will use the runway;
- the maximum weight of aircraft (as weight
increases, so the length of runway required increases);
- aircraft trip length (longer trips require
more fuel, and hence heavier weights);
- airport elevation (the higher the elevation
above sea level the less the atmospheric pressure, the less the lift and
the longer the runway required);
- airport temperature (the higher the temperature,
the thinner the air, the less the lift and the longer the runway required);
- surface winds (headwinds decrease the take-off
length, tailwinds increase the take-off length);
- runway gradient; and
- runway surface (smooth asphalt means shorter
take-off length than grass).
Average runways for major airports are about 2500 to
3500 m in length, when the airport is at sea level.
LINKS TO SITES ON AIRPORTS.
The
Airline and Airport Links.com
site contains links to the home pages of a lot of airports around the world.
The Australian airports accessible from this site include Brisbane, Melbourne,
Sydney and Perth. There is also a link to the new Chek Lap Kok airport in
Hong Kong which opened on 6 July 1998. (However info from the Hong Kong site
appears to take a fair while to download).
Planning and development of a new airport can be
a very lengthy task. This is well illustrated by the attempts to select a
site for Sydney's second airport. The history of the proposal is detailed
in a Parliamentary Background Paper '
Second Sydney Airport - A Chronology
' by Paula Williams.
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17.4 Water Transport
Water transport is one of the oldest forms of transport.
The colonisation and early development of Australia were greatly influenced
by water transport. In fact, shipping has always been a vital lifeline for
the island continent of Australia.
Goods moved by sea may be categorised into:
- dry bulk cargo;
- liquid bulk cargo; and
- general cargo.
The size of a ship is expressed in tons. There are
different methods of assessing tonnage; the common methods being:
- Displacement tonnage – the weight of water the
ship displaces in accordance with Archimedes’ Principle. This equals the
total weight of the ship plus all that it contains.
- Deadweight tonnage – a measure of the load that
the ship is designed to carry, i.e. cargo, passengers, stores, etc. This
is the difference between the displacement tonnage when the ship is fully
loaded and unloaded.
- Gross Registered tonnage (GRT) – a measure of
the total cubic capacity of all enclosed space. In this case the ton is taken
as 100 cubic feet.
- Net Registered tonnage (NRT) – the gross registered
tonnage less space required to run the ship e.g. machinery space, crew’s quarters,
etc.
For efficient ship operation the time spent both at
sea and in port must be kept to a minimum. Speed of operation depends on
the technical design of the vessel. Speed of port operation requires high
level of mechanisation. This may be difficult to achieve for general cargo
as there is a need for different equipment for different goods.
The development of specialist ships such as bulk
cargo ships, and the introduction of containerisation has helped to achieve
greater port efficiency for loading and unloading ships.
17.5 Ship Types
Road, rail and air vehicles feature a high degree of
standardisation and are usually produced using a mass-production system. Ships,
on the other hand, are not mass-produced and usually feature a high degree
of individuality. Even ‘sister ships’ are unlikely to be exactly the same.
However ships do fall into a relatively small number
of distinct groups, usually related to the task which they are designed to
perform. Some of the common types of commercial ships are:
- General Cargo Ships. Generally these are of
modest size, mostly under 15,000 GRT. They ‘fill the gaps’ left by more specialised
vessels, but are still the most common type of vessel for goods transport.
One advantage of general cargo ships is that they can be switched between
different types of haulage, and therefore may have a greater usability than
more specialised vessels.
- Container Ships. These vary greatly in size,
depending largely what route they are operating. Ships operating on larger
international routes would often have a capacity of 2000 containers, of which
about 300 would be carried as deck cargo. Smaller ships used on shorter routes
may have a capacity of only 300 containers. The ships may be provided with
gantry cranes if they are likely to use ports inadequately equipped with heavy
lifting gear. Because of their high volume, high speed and relatively high
port turnaround, container ships can carry many times the cargo of a general
cargo ship in a year.
- Large Crude Carriers. The largest of these vessels
are known as Very Large Crude Carriers (VLCC) and Ultra Large Crude Carriers
(ULCC). These ships range in size from 250,000 to 400,000 tons and are designed
to operate from oil-producing countries to a limited number of ports in consuming
countries. Design is based on ensuring stability of the large volume of liquid
cargo. To prevent excessive surging of the liquid when the ship rolls and
pitches, a series of separate compartments is used to hold the liquid. A
feature of tanker operation is their relatively quick turnaround and they
consequently can spend a large proportion of their time at sea.
- Dry Bulk Carriers. In concept these are similar
to large crude carriers, although they are usually less than 200,000 dwt
(deadweight tons).
- Ro-ro Ships. Roll-on, roll-off ships are designed
to minimise the time of loading and unloading of general cargo by allowing
it to be driven on and off the vessel. Loading is generally through a stern
door with ramps to different levels. Some ships will also incorporate an opening
bow which permits a movement of vehicles through the vessel. Ships of this
type may need specialist port facilities, although the need for complex lifting
equipment is dispensed with.
LINK TO THE PICTURE GALLERY
The Picture Gallery contains photographs relating to
Shipping
.
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17.6 Liner Trades and Shipping Conferences
A liner service is one which offers regular
scheduled services on fixed routes. They can generally handle a range of cargo,
and may use general cargo or container vessels.
Where several liner companies operate over the same
route, it is common for them to form an association known as a conference
. Basically, a conference is simply a meeting of all the liners serving any
particular route, for the purpose of achieving a regular pattern of sailings
to give the maximum service to shippers and to reach common agreement on rates.
Conferences range from informal agreements to well
developed organisations with permanent secretariats. Shippers rely on liner
services for their transport needs, just as the shipping lines depend on
the shippers for their trade. This mutual support is necessary if liner operators
are to make large investments in new ships. To make such investments liner
operators desire protection against competitors who might undercut prices
for a relatively short time and then disappear from the business. Hence the
voluntary system of liner conferences has evolved.
Conferences may be 'open' where entry is not
restricted but where new members must adhere to freight rates, or 'closed
' where entry is limited by the conference itself. Because of the monopolistic
nature of conferences, Australian shipping conferences require exemption by
the Federal Government from the restrictive trade provisions of the Trade
Practices Act.
17.7 Ports and Harbours
A harbour is a partially enclosed area of water
which serves as a safe refuge for ships. They are used as areas of accommodation
for protection during storms, and for replenishing supplies, loading and
unloading cargo, and repairs.
The term port refers to a portion of a harbour
which acts as the base for commercial activities.
Harbours may be classified into the following broad
categories:
- natural harbours, where protection is offered
by natural topographical features;
- seminatural harbours, where protection is given
on the sides by land but which require artificial protection to be constructed
at the entrance; and
- artificial harbours, where construction of breakwaters
and jetties is required to provide suitable protection against wave action.
To fulfil its function a harbour must satisfy three
basic requirements:
- sufficient depth for the size of vessels
to be accommodated;
- protection against destructive wave action;
and
- the bottom should furnish a secure anchorage.
The selection of a harbour site should aim to find
a suitable location that will offer shelter, convenience and ease of operation.
Convenience includes the potential to establish shore based port facilities.
Investigation for harbour sites must collect information
on the following aspects:
- wave exposure – height, direction and frequency
of occurrence;
- natural protective features;
- water depth;
- sediment movement;
- tide range;
- land base area available; and
- expansion potential.
LINK TO THE PICTURE GALLERY
The Picture Gallery contains photographs relating to
Port Facilities
.
LINKS TO SITES ON PORTS
The Sydney
Ports Australia
Web site contains a lot of information about the port facilities available
in Sydney. In particular, details of all docking and storage facilities are
given in the Sydney Harbour Directory and the Botany Bay Directory within
the "Port Facilities" link.
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Page last modified 24 June 2002.